This invention relates to compliant hydrodynamic fluid film bearings, and more particularly to an improved compliant support element for a bearing of this type.
A compliant hydrodynamic fluid film bearing is a thin, lightweight, inexpensive structure that supports extremely high speed rotors on a fluid film with small frictional losses, good damping characteristics, excellent durability and reliability. It includes a thin, flexible bearing sheet supported on a compliant support element which, in turn, is supported on a stationary mounting member such as a bearing sleeve or a thrust plate.
The hydrodynamic fluid film which supports the rotor on, and separates it from, the bearing sheet is created by the viscous or shear forces acting in the fluid parallel to the direction of relative movement between the rotating rotor bearing surface and the bearing surface of the bearing sheet. A rotating thrust runner, for example, drags the boundary layer of fluid with it as it rotates over the bearing sheet. The boundary layer, in turn, drags in the layer of fluid immediately adjacent and in this way a velocity gradient is established in the fluid in the gap between the thrust runner and the bearing sheet. This gap is wedge-shaped, tapering in the direction of movement of the rotating rotor. The wedge-shaped gap is inherent in the journal bearing and is created in the case of the thrust bearing by various techniques. The pressure of the fluid drawn into the wedge-shaped gap tends to increase toward the narrow end of the gap, thus creating the pressurized cushion or fluid film which dynamically supports the rotating rotor.
The compliant support element for the flexible bearing sheet enables it to conform to the bearing surface of the rotating rotor despite thermal distortion and centrigual growth, and despite rotor run-out due to eccentric loads or rotor unbalance. In prior art rigid hydrodynamic fluid bearings, these effects can interfere with the conformance of the stationary bearing surface with the bearing surface of the rotating rotor and thereby adversely affect the hydrodynamic action by which the supporting fluid film is generated. The compliant support element in compliant hydrodynamic bearings can deflect and expand to support the bearing sheet in correct hydrodynamic relationship to the rotating rotor despite these deviations of the rotor bearing surface from its normal plane of operation. The pressurized fluid cushion or film on which the rotor is supported obviates the need for rolling element bearings, and the self-pressurizing nature of this bearing frees it from dependence on external pressurizing equipment needed in hydrostatic bearings. Thus, this bearing offers the potential advantages of a virtually limitless speed ceiling, a miniscule wear rate, and long reliable operation.
Because of these advantages, the compliant hydrodynamic fluid bearing has attracted a great deal of attention in the recent past for extremely high rotational speed applications. In addition, when the lubricating fluid used in these bearings is a gas such as air or helium, the temperature limitations imposed upon conventional bearings by reason of the coking temperature of oil or other liquid lubricants does not apply and the temperature limitation then becomes that of the metal elements in the bearing. These and other properties make these bearings extremely attractive for applications such as turbomachinery, high speed industrial applications, and certain consumer products.
There is one limitation, however, which has in the past restricted the use of these bearings to fewer fields than their potential application. The relatively low yield strength of the thin and flexible materials used in these bearings to achieve the desired compliance have imposed a limited load carrying capacity. The performance characteristics of these bearings, well known to experts in the field of high speed rotating machinery, have inspired continuous research to discover ways to increase the load carrying capacity of these bearings in order to apply them to higher load applications. These approaches have generally involved increasing the gauge of the bearing materials or adding other stiffening or strengthening members. These expedients have produced an increase in load carrying capacity but, have usually been accompanied by other undesirable effects such as a decrease in compliance and therefore a decrease in the tolerance of the bearing to misalignment and transient rotor excursions referred to above.